The fourth annual iHeartRadio Music Festival lineup was announced Wednesday – and it's packed with the industry's finest.

"People can expect a weekend that they will never forget," festival host Ryan Seacrest told PEOPLE at the Clear Channel Media and Entertainment offices in New York on Wednesday. "I saw the list coming together, and I was so excited to announce it because it covers everything in music – all these artists in one place for the weekend and the biggest fans who make the pilgrimage who come to see them."

The genre-spanning mega-concert, slated for Sept. 19 and 20 in Las Vegas, will feature performances by Taylor Swift, Coldplay, Usher, One Direction and more and, as in the past, will highlight surprise collaborations.

"We literally want them to happen and no one know about them [beforehand]," Seacrest said. "We sneak an artist in, and all of a sudden, they're on stage. It creates this magic."

Though the collaborations are under wraps, one thing fans can expect is new material from Taylor Swift: The singer's follow-up to 2012's Red is due this fall, and Tom Poleman, president of national programming platforms for Clear Channel, confirms she'll be performing new music.

"These artists are all at the top of their game," Seacrest said. "They do this for a living; they're doing it every night on tour – but they also know that the other artists there are doing it are there and will be watching. So they try and change it up, amp it up a little. All eyes are on them."